NGC 6888, the Crescent Nebula
Natural color composition from the emission of ionized elements, R=80%Hydrogen+20%Sulfur, G=100%Oxygen and B=85%Oxygen+15%Hydrogen to compensate otherwise missing H-beta emission. This composition is very close to a visual spectrum.
Star colors are mixed from the NB channels, Red=H-a, G=O-III and B= 85%O-III + 15%H-a.
The Crescent Nebula, also known as NGC 6888, Caldwell 27 and Sharpless 105, is an emission nebula in constellation Cygnus, about 5000 light years distance.
It is formed by the fast stellar wind from the Wolf-Rayet star, WR 136 (HD 192163), colliding to an slower moving wind ejected by the same star when it became a red giant, around 400.000 years ago.
The result of the collision is a glowing shock shell around the star. Apparen size of the shell is 18' x 12' and the real size is about 25 x 16 light years.
This image was selected to National Geographics "Daily Dozen"
Optics Meade LX200 GPS 12" forced to @ f4.65
Guiding with SXV-AO active optics unit 11Hz
Baader H-alpha 7nm, 4.5h 20min subs
Baader O-III 8,5nm 2h 40min 20min subs binned 2x2
Baader S-II 1h 5 min subs binned 3x3